In traditional passive antenna systems, only one sector can be supported on an antenna at a single carrier frequency. The beam shape of all sectors from the passive antenna is typically fixed by a combination of the antenna element structure and the corporate feed network that applies the signal to the individual antenna element feeds. In order to combat the disadvantages of passive antenna systems, active antenna array systems (AAS) have been developed. An AAS is generally created by integrating several radio frequency (RF) components (e.g. power amplifiers, transceivers, couplers, etc.), which are conventionally considered as part of a base station, with the antenna's radiating elements. This enables the phase and amplitude of the signals from each radiating element inside the antenna to be electronically controlled, using signal processing to shape and steer the direction of the radiated beam. The direction can be controlled in both a vertical and horizontal azimuth, and this technique is more generally referred to as beamforming.
Vertical beamforming can be used to create a plurality of beams with at least one beam dedicated per cell sector, and where the beams are directed to different geographic regions away from the antenna. In creating two dedicated cell sectors with a passive antenna arrangement, sector area hardware resources may be doubled. Currently, the known ways of providing different ‘tilts’ of the antenna beams using conventional passive antennae other than utilise separate antenna arrays. An alternate means is to partition an antenna array to create a subgroup of antenna elements to act on a separate sector, where each subgroup would process beams dedicated to an individual cell sector.
These two techniques to provide different tilts have a number of disadvantages associated with them. For example, in the case of utilising separate antenna arrays to act on different sectors, a duplication of antenna units will need to be deployed to provide the same performance. This results in increased costs in terms of installation time, antenna tower real estate requirements and coaxial feeder cable to separate radio units as part of the infrastructure deployment.
Further, in the case of the antenna array being sub-partitioned, the effective beam width that can be produced by the array is increased, thereby increasing an overlap region between adjacent sectors. A yet further disadvantage is that, as the array becomes divided between sectors, there is a proportionate reduction in available antenna gain.
In Antennas and Propagation (EUCAP), 2012 6th European Conference, Page(s): 2789-2793, a use of an array for outputting vertical sectorisation beams is discussed. This document does not consider embodiments of beam signal processing synthesis or of how a calibration scheme for an antenna array supporting such vertical sectorisation beams could be supported.